Declaration and use of php functions

* Function

* 1. Declaration syntax;

* 2. Calling method;

* 3. Parameter setting;

* 4. Return value;

* 5. Scope

//Declaration

function hello() //无论有无参数,圆括号不能省略
{
    echo '欢迎来到php中文网学习';
}

//Call: call by name, must bring parentheses

hello();
echo '<hr>';
//可以设置参数
function hello1($siteName)
{
    echo '欢迎来到'.$siteName.'学习';
}

//You must bring parameters when calling now

hello1('php中文网');
hello1('www.php.cn');

//If you forget to give parameters when calling, you can give the function parameters a default value

function hello2($siteName = 'php中文网')
{
    echo '欢迎来到'.$siteName.'学习';
}
echo '<hr>';

//You can pass parameters when calling now , you can also pass no parameters

hello2();
echo '<br>';
hello2('PHP中文网_www.php.cn');

//If there are multiple parameters, the default value should be written to the end

function hello3($name ,$siteName = 'php中文网')
{
    echo '我是'.$name.',欢迎来到'.$siteName.'学习';
}
echo '<hr>';

//Calling method

hello3('peter zhu'); //第一个参数没有默认值,必须传参
echo '<br>';
hello3('peter zhu', 'www.php.cn'); //实参与形参的位置必须一一对应
echo '<hr>';

//Scope : Function internal variables cannot be accessed from the outside. Similarly, external variables cannot be accessed from inside the function.

$siteName = 'php中文网';

//External variables, or global variables, will automatically become an element in the global variable array $GLOBALS. The variable is The key name of the element

echo $GLOBALS['siteName']; //它里面的数据就是变量siteName中的值,而且这是一个超全局变量,可以在函数中使用
function hello4()
{
    $name = 'peter zhu';
//    return $siteName;
    return $GLOBALS['siteName'];
}
echo hello4();
echo '<br>';
echo $name; //外部是访问不到函数内的变量的,除非函数将这个变量返回到外部